1. Field of the Invention
The present invention is a novel catalytic process for making hydrofluoroalkene from a hydrofluoroalkanol in high yield using a dehydrating agent and in the presence of a catalyst. More particularly, it relates to making CF3CF═CH2 from CF3CF2CH2OH in high-yield using methane as the reducing agent in the presence of a transition metal catalyst.
2. Discussion of the Background Art
2,3,3,3-tetrafluoro-1-propene (R1234yf), which is a probable candidate for low global warming potential refrigerant, has been synthesized by pyrolysis of methyl chloride and tetrafluoroethylene or chlorodifluoromethane. In a reaction, 55 cc./min. MeCl and 110 cc./min. CHClF2 is passed through a Pt tube 6 mm.×24 in. heated to 800° C. The gaseous products are scrubbed free of HCl and dried to yield only a small amount (14.8 mole-%) of 2,3,3,3-tetrafluoropropene. This process is a low yield process and because of the conversion of pentafluoropropanol obtained in our hand is as high as 100%, almost 90% of the starting material is lost to unimportant byproducts including a sizeable amount of carbon black.
On the other hand, 2,3,3,3-pentafluoro-1-propanol, which is generally synthesized by the reaction of tetrafluoroethylene, formaldehyde, and HF in the presence of TiF4 as the catalyst and limonene as the polymer inhibitor, can serve as a starting material to synthesize 2,3,3,3-pentafluoro-1-propene (R1234yf). It has been shown previously that fluorine-containing olefins CH2═CFRf[Rf=(per)haloalkyl group)] are prepared at low cost and low toxic waste generation by high-temperature dehalohydrogenation and dehydration of fluoroalcohols such as HOCH2CF2Rf in the presence of H2 gas. Feeding an activated C-packed tube at 500° C. with a 1:3 (mol/mol) mixed gas of HOCH2(CF2)4H and H2 with a residence time of 4 sec yielded CH2:CF(CF2)3H at monomer conversion 64% and selectivity 82%. This is a high-yield process; however, for a plant level production, the handling of H2 at high temperature raises serious safety related questions.
Also, one needs to couple a H2 plant on site with the 1234yf plant. This requires high installment cost. Thus, there is incentive to look for an alternative catalytic process scheme involving an alternative reducing agent instead of hydrogen.
The present invention also provides many additional advantages, which shall become apparent as described below.